This invention relates to plant defense from parasites, including fungi and bacteria, by means of copper compounds. Examples of plant diseases on which the invention is effective are: botrytis, plasmopara viticola, uncinula necator, cercospora beticola, venturia pirina, venturia inaequalis, clasterosporium carpophilum, coryneum beyerickii, alternaria solani, taphrina deformans, exoascus deformans, sclerotinia fructigena, puccinia graminis, gymnosporangium, phragmidium subcorticum, bacillus phytophorus, psedomonas solacearum.